MCBs

MCBs, or miniature circuit breakers, are a type of switch used to automatically turn off electrical circuits during abnormal conditions. MCBs often replace fuses in low voltage electrical circuits as they can be more reliable, much more sensitive and are resettable.

How an MCB Works

When continuous overcurrent flows through an MCB, a bimetallic strip is heated and causes it to bend. This bending of the bimetallic strip releases a mechanical latch opening the contacts and turning off the MCB, thereby stopping the current to flow in the circuit. To restart the flow of current the MCB must be manually turned on. This mechanism protects the MCB from faults arising due to overcurrent or overload and is intended to prevent the accidental overloading of the cable in a no-fault situation. The speed of the MCB tripping will vary with the degree of the overload. This is usually achieved by the use of a thermal device in the MCB. The second characteristic is the magnetic fault protection, which is intended to operate when the fault reaches a predetermined level and to trip the MCB within one-tenth of a second. The level of this magnetic trip gives the MCB its type characteristic.

MCBs are used to perform many functions such as local control switches, isolating switches against faults and overload protection devices for installation or specific equipment or appliances.

MCB Types

MCBs have three common types for circuit protection in residential, commercial and industrial applications. The use is classified by a type, which determines the tripping characteristics of the MCB:

Type B - trips between 3 and 5 times the load current

This type will trip instantly at a rate of three to five times its rated current. These are normally used for resistive or small inductive loads where switching surges are very small. Therefore, these are suitable for residential or light commercial installations.

Type C - trips between 5 and 10 times the full load current

This type will trip instantly at a rate of five to ten times its rated current. These are normally used for high inductive loads where switching surges are high such as small motors and fluorescent lighting. In such cases, type C MCBs are preferred to handle higher value of short circuit currents. Therefore, these are suitable for highly inductive commercial and industrial installations.

Type D - trips between 10 and 20 times the full load current

This type will trip instantly at a rate of ten to twenty-five times its rated current. These are normally used for very high inductive loads where high inrush current is very frequent. These are suitable for specific industrial and commercial applications. The common examples of such applications include x-ray machines, UPS systems, industrial welding equipment, large winding motors, etc.

How to select a suitable MCB for the application?

Focus on 3 main points to choose the right MCB for the electrical circuit

  1. Ampere rating
  2. Short circuit breaking capacity
  3. Application type

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Description Price Number of Poles Current Rating Model Number Range Series Rated AC Voltage Tripping Characteristics Breaking Capacity Mounting Style Rated DC Voltage Length Width Depth Application
RS庫存編號 521-4951
製造零件編號5SY6104-7
BrandSiemens
HK$155.93
單位
1 4 A - Sentron 5SY6 230 V, 400 V Type C 6 kA - - 89.8mm 17.6mm 76.4mm -
RS庫存編號 746-7699
製造零件編號S202-C2
BrandABB
HK$406.81
單位
2 2 A - System M Pro S200 400 V Type C 6 kA - - - 35mm 69mm -
RS庫存編號 776-3073
製造零件編號A9N18367
HK$4,990.59
單位
3 100 A - Acti 9 C120N 440 V Type C 10 kA, 20 kA - ≤375V 81mm 73mm 81mm -
RS庫存編號 791-3293
製造零件編號A9F54110
HK$207.63
單位
1 10 A - Acti 9 iC60H 12 → 60 V, 100 → 133 V, 220 → 240 V Type C 10 kA DIN Rail 12 → 48 V, 72 V 85mm 18mm 78.5mm -
RS庫存編號 776-3345
製造零件編號A9F76106
HK$540.00
單位
1 6 A - Acti 9 iC60N 240 V Type B 10 kA - 72V 18mm - 85mm -
RS庫存編號 734-9295
製造零件編號A9F87216
HK$1,009.01
單位
2 16 A - Acti 9 iC60H 12 → 60 V, 100 → 130 V, 220 → 240 V, 380 → 415 V, 400 V, 440 V Type C 10 kA - 12 → 144V - - - -
RS庫存編號 734-9276
製造零件編號A9F77263
HK$1,491.18
單位
2 63 A - Acti 9 iC60N 12 → 60 V, 100 → 130 V, 220 → 240 V, 380 → 415 V, 400 V, 440 V Type C 6 kA - 12 → 144V - 36mm - -
RS庫存編號 539-8267
製造零件編號2CDS211001R0404
BrandABB
HK$124.12
單位
1 40 A - System M Pro S200 440 V Type C 6 kA - 60V 85mm 17.5mm 69mm -
RS庫存編號 488-7457
製造零件編號2CDS251001R0065 - S201B6
BrandABB
HK$130.51
單位
1 6 A - System M Pro S200 253 V Type B 6 kA - 72V 88mm 17.5mm 75.8mm -
RS庫存編號 746-8107
製造零件編號2CDS274001R0635
BrandABB
HK$1,141.07
單位
4 63 A - System M Pro S200 400 V Type B 10 kA - - 83mm 70mm 74.8mm -
RS庫存編號 539-8223
製造零件編號2CDS211001R0164
BrandABB
HK$119.32
單位
1 16 A - System M Pro S200 440 V Type C 6 kA - 60V 85mm 17.5mm 69mm -
RS庫存編號 791-3344
製造零件編號A9F54216
HK$599.92
單位
2 16 A - Acti 9 iC60H 12 → 133 V, 220 → 240 V, 380 → 415 V, 440 V Type C 10 kA DIN Rail 100 → 133V 85mm 36mm 78.5mm -
RS庫存編號 734-9450
製造零件編號A9N21369
HK$739.71
單位
1 + N 32 A - Acti 9 DT40 400 V Type C 6 kA - - - - - -
RS庫存編號 383-2024
製造零件編號5SY4110-7
BrandSiemens
HK$163.94
單位
1 10 A - Sentron 5SY4 400 V Type C 10 kA - - 89.8mm 17.6mm 76.4mm -
RS庫存編號 776-3216
製造零件編號A9N61534
HK$1,334.50
單位
2 30 A - Acti 9 C60H-DC - Type C 20 kA - 500V 36mm 73mm 81mm -
RS庫存編號 746-7637
製造零件編號S204-B63
BrandABB
HK$1,393.63
單位
4 63 A - System M Pro S200 400 V Type B 6 kA - - - 70mm 69mm -
RS庫存編號 825-5712
製造零件編號P1MB2PC06
BrandLovato
HK$322.61
單位
2 6 A - ModuLo P1MB 230 V, 400 V Type C 10 kA - 80V 86.5mm 36mm 79.52mm -
RS庫存編號 791-3297
製造零件編號A9F54116
HK$185.98
單位
1 16 A - Acti 9 iC60H 12 → 60 V, 100 → 133 V, 220 → 240 V Type C 10 kA DIN Rail 12 → 48 V, 72 V 85mm 18mm 78.5mm -
RS庫存編號 734-9440
製造零件編號A9N21364
HK$661.92
單位
1 + N 6 A - Acti 9 DT40 400 V Type C 6 kA - - - - - -
RS庫存編號 791-3385
製造零件編號A9F54306
HK$860.29
單位
3 6 A - Acti 9 iC60H 12 → 133 V, 220 → 240 V, 380 → 415 V, 440 V Type C 10 kA DIN Rail 100 → 133V 85mm 54mm 78.5mm -